You will need to find out what the output impedance of the Janus pre is spec'ed at. Some tube pres have a fairly high one and Pass amps have a relatively low input impedance. You would want the input impedance of an amp to be 10 times greater (or more, general rule) than the preamps spec.
Right now I am listening to a Conrad Johnson tube pre going into a Pass XA30.5 with excellent results. The CJ (a CT-5) has an output of 800 ohms and the Pass's rca input is close to 20k (I have to use the rca's) so I'm at a 25 to 1 ratio.
Chances are good that you will be fine unless the Janus output is abnormally high.
Right now I am listening to a Conrad Johnson tube pre going into a Pass XA30.5 with excellent results. The CJ (a CT-5) has an output of 800 ohms and the Pass's rca input is close to 20k (I have to use the rca's) so I'm at a 25 to 1 ratio.
Chances are good that you will be fine unless the Janus output is abnormally high.